This invention relates to a frequency discriminating circuit for discriminating a plurality of signals of different frequency.
In a channel up/down control or a volume up/down control in a remote control type receiver, up and down control signals of different frequencies are provided by the control section, and the frequencies of the control signals are discriminated on the receiver side. For this purpose, a frequency discriminating circuit for discriminating the frequencies of the two signals is employed.
FIG. 1 shows one example of a conventional frequency discriminating circuit which comprises capacitors C.sub.1 and C.sub.2 for cutting off the DC components of the input signals, active filters 1 and 2 having selectivity characteristics corresponding to the frequencies of the input signals, rectifier circuits 3 and 4 for rectifying the outputs of the filters, and output transistors Q.sub.1 and Q.sub.2. These circuit elements are provided separately according to the two input signals of different frequency, in this case. The input signals are detected by the filters 1 and 2 corresponding to the frequencies thereof, and are then rectified by the rectifier circuits 3 and 4, to thereby drive the output transistors Q.sub.1 and Q.sub.2, respectively. However, when two signals at levels higher than certain values are inputted simultaneously, or when the difference in frequency between two input signals is small, or when the selectivity characteristics of the filters 1 and 2 are broad, then the two output transistors Q.sub.1 and Q.sub.2 may be turned on at the same time, which causes erroneous operation.